The invention relates to optical elements composed of plastics and suitable for applications in regions with stringent fire safety regulations, and to uses of the optical elements of the invention. These regions with stringent fire safety regulations are in particular aircraft interiors or else ships, where it can usually be difficult for the passengers to escape in the event of a fire. Components used in such conveyances are therefore subject to particular fire protection regulations, set out in the corresponding standards or specifications. Particularly relevant standards for aircraft are JAR/FAR 25.853a, JAR/FAR 25.869 and ABD0031.
Plastics resistant to high temperatures are known from the prior art, an example being polyphenylene sulphide, which is said to be stable in prolonged use at temperatures up to 200° C. and to withstand brief exposure to temperatures of up to 240° C. It is flame-retardant to the German DIN 4102 standard, i.e. it is self-extinguishing once the source of ignition has been removed.
DE 39 00 674 A1 likewise describes plastics resistant to high temperatures and based on copolymers of polysulphone and polyimide, these being suitable for prolonged exposure in the range from 150° C. to 180° C.
However, an intrinsic feature of all of these plastics is that although they are to some degree transparent they have a yellow colour clearly discernible by the naked eye, and cannot therefore be used as material for optical elements for passage of light in the visible region for spectrum. For this reason, by way of example, the outer panes of aircraft windows are manufactured from polymethyl methacrylate (PMMA), for which exceptional approval has been given, this material also being known by its trade name Plexiglas. This is a transparent material which is substantially colourless, but not flame-retardant. This compromise is accepted because windows with a clearly discernible colour are considered likely to be unpopular with passengers.
The mirrors in aircraft bathrooms are moreover not currently manufactured from plastics, but from polished aluminium, an attendant disadvantage of which is that the actual polishing process has high production cost. A polished aluminium surface is also susceptible to scratching, and the mirrors in aircraft bathrooms therefore require frequent replacement. This replacement is another noticeable adverse feature of airline operating costs.
Glass cannot be used as material for these applications in passenger aircraft, because laminated glass would be required in order to meet requirements for preventing injuries caused by glass splinters, and this type of glass is heavy, and reduce payload, or would undesirably increase operating costs.